West Shore Cardiology

Transcription

1 West Shore Cardiology Stress Testing The use of stress testing for the diagnosis of previously undiagnosed CAD in the symptomatic patient as well as following those with known CAD is a commonly used test. However, choosing the right test for the right patient is often a challenge. There are really 5 main choices: Regular stress ECG, an exercise or persantine (Lexiscan) myoview, and an exercise or dobutamine echocardiogram. In order to know what test is the best for which patient, one must have a general idea of the strengths and limitations of each test. In general (and even us cardiologists are often guilty) we probably don t order enough regular GXT s. The guidelines recommend a regular GXT in younger patients with no previous history of CAD, low pretest likelihood of disease, able to ambulate and with a normal resting ECG (i.e. no LBBB, significant resting ST changes, paced rhythm, or WPW). Important information to know when determining what type of stress test to order and knowing what to do with the results is knowing the patients pretest likelihood of disease as well as the sensitivity and specificity of the test and how these three things interact to give a positive or negative predictive value of a positive or negative test result. The sensitivity is the likelihood of the test being positive in the face of disease where specificity is the likelihood of the test being negative in the absence of disease. In general, higher sensitivity is obtained at the expense of lower specificity and vice versa. Let s take the example of a 40 y.o. female with atypical chest pain who has a pretest likelihood of disease of only 5%. She undergoes a stress myoview (with a sensitivity of 90% and specificity or 80%) and the test is positive. Despite these positive results, the positive predictive value (i.e. the likelihood she actually has disease) is still only 19% with an 81% likelihood this was a false positive result. On the other end or the spectrum would be a 70 y.o. male with typical angina and therefore a 90% pretest likelihood of disease. A positive test only confirms what you already know, however, there may still be significant prognostic information obtained from the test. If the test is negative, however, it s likely a false negative. The most bang for your buck is the patient with an intermediate (say 20 80% range) pretest likelihood of disease (i.e. 50 y.o. male with atypical symptoms or 40 y.o. female with typical angina). Determining the pretest likelihood of disease takes into account the patients symptoms as well as their overall risk for heart disease. This is clearly not an exact science. I've included some tables to help in determining a patient's risk. For the purpose of classifying patients, the quality of their chest pain is described as being "typical angina", "atypical angina", or "nonanginal chest pain". (see definitions in figure 1). Once the characteristic of the patient's chest pain is determined, one can use Figure 2 and 3 to help determine likelihood of disease. Figure 2 is purely based on age and sex while figure 3 gives a range based on whether the patient has DM, hyperlipidemia and smokes or not. In a patient with a low pretest probability of obstructive CAD (i.e. young patient with minimal risk factors, atypical CP) the ACC guidelines give a IIa recommendation (i.e. it s reasonable to do) for a regular GXT (no imaging). For this same low probability patient they give a IIb recommendation (i.e. may be considered) for a stress echo and a level III (NOT recommended) for a stress nuclear study. The ACC and American Society of Nuclear Cardiology have published Appropriate Use Criteria (AUC) for stress testing and classify a stress myoview for this low risk patient as Inappropriate. For a patient with an intermediate to high

2 likelihood of disease an exercise nuclear or echo is felt to be a reasonable test. In a patient unable to exercise or with an uninterpretable ECG, an imaging test is obviously recommended. If you ve decided to proceed with a stress imaging study, you then need to decide between a stress nuclear or a stress echo. In general, the stress nuclear is going to be a little more sensitive and a little less specific than a stress echo. This means that the nuclear test is a little more likely to find disease if present than the stress echo, but you re also more likely to have a false positive test due to artifact. The echo is also very dependent on the quality of the images obtained and is probably not the procedure of choice in our morbidly obese patients or those with significant COPD. The other downside of the nuclear study is obviously the radiation exposure. In general, the amount of radiation in a standard myoview varies from 6 to 15 milliseiverts. This is about equivalent to a CT angio study. Dr. Nancy Brenneman has been working on an initiative to minimize the radiation on our younger patients by not bringing them back for resting images if the stress images are normal. This may be a reason to order a stress echo in your younger patients in whom you are more concerned about the lifetime risk of radiation exposure. As you know we do many more myoview studies than stress echos. We have been performing and interpreting nuclear scans for many years and think we do a good job. This is reflected by the fact that our normal catherization rate is significantly less than the national average. In general, as a group, we tend to favor nuclear over echo if you are going to order an imaging study. If the patient has known CAD (particularly a previous intervention or MI) or if they have a depressed EF, we feel nuclear is clearly preferable. On the other hand, a stress echo is a very reasonable test for a younger patient who s not high risk and has good quality echo images (i.e. not morbidly obese or severe emphysema). I often see patients referred for pharmacological stress testing (dobutamine echo or lexiscan myoview) when they are perfectly able to ambulate. Performing a pharmalogical stress test on a patient able to ambulate is actually a level III recommendation (i.e. Not recommended). Often we will change the test to exercise but realize that it s always preferable for a patient to exercise. There is significant prognostic information gained by having a patient walk on the treadmill. The other issue that often comes up is whether or not to have a patient hold their beta blocker. In general, if the goal of testing is to diagnose the presence of CAD, you would likely hold the beta blocker to maximize the diagnostic accuracy of the test. On the other hand, if the patient has known CAD and the purpose of the test is to determine whether they have ischemia while on medical therapy you would want the test on beta blockers. Lastly, you may be familiar with the Choosing Wisely initiative by the American Board of Internal Medicine along with multiple other specialty societies to try and decrease the amount of unnecessary testing and procedures. Each society has been asked to come up with five procedures or tests in certain patients that are felt to be unnecessary or potentially harmful. Three of the five from the ACC (American College of Cardiology) have to do with stress testing and I thought I would include them as well. They recommend not performing stress cardiac imaging in: 1) patients without cardiac symptoms unless high risk markers are present; 2) as part of routine follow up in asymptomatic patients (i.e. at the one or two year anniversary of a cardiac procedure. An exception may be for patients more than five years after a bypass operation); and 3) as a pre-operative assessment in patients scheduled to undergo low-risk non-cardiac surgery.

3 Take Home Points Estimate the pretest likelihood of disease in patients based on age, sex, symptoms and risk factors before ordering stress tests. Realize that the positive and negative predictive value of a stress test result is strongly influenced by the patients pretest likelihood of disease. Stress test are most helpful in patients with an intermediate pretest likelihood of CAD (i.e % range) Strongly consider regular GXTs in patients with low likelihood of disease who have normal ECG s and can exercise. Consider imaging GXTs in patients with intermediate or high likelihood of disease. Stress echo best in younger patients (no radiation), non-obese, with no previous CAD and with normal baseline LV function. Nuclear best in patients with previous interventions, MI or depressed EF. Also better in obese patients and those with severe emphysema (in whom echo images would likely be compromised). Always exercise if possible. Reserve pharmacological stress for those who truly can t exercise.

4 West Shore Cardiology Suspected Ischemic Heart Disease Able to Exercise NO Low probability Younger YES No previous CAD Good echo images We prefer YES Known CAD and/or Myoview LV dysfunction NO YES NO Lexiscan Myoview Dobutamine Pretest Probability of Disease Echo Low/Intermediate Intermediate/High Interpretable ECG We generally favor Nuclear. Consider stress echo in YES NO Younger patients, lower risk, and good images Regular GXT Stress Echo Consider stress echo Nuclear is Level III Recommendation (i.e. Not recommended)

5 Fig. 1 Fig. 2 Fig. 3